Think
you've got gas problems? Then consider the Atlantic ocean near Namibia,
in southern Africa. Every so often, a massive hydrogen sulfide gas eruption
from the ocean floor kills fish, exposes local people to a major rotten
egg stench, and causes ecological havoc in the ocean.

The aroma of rotten eggs is familiar to neighbors
of industrial plants, but it can also arise naturally when organic stuff
rots in the absence of oxygen, as at volcanic vents.

Along Namibia's coast, eruptions of hydrogen sulfide
are a regular feature, although they're not featured in scratch-and-sniff
tourist brochures. The eruptions are not entirely miserable from some
perspectives.

Although millions of fish may die, scavenging birds
feast on their carcasses.

Namibians also feast on lobsters escaping to shore
from the oxygen-deprived water, where they are easy game for beachcombers.

Got my eye on you! Now,
for the first time, the disturbance has been tracked from space -- and
it turns out to be inordinately large. "What shocked the Namibians and a
lot of the scientific community was the frequency, spatial extent, and how long these
events could last," says Scarla Weeks, a research associate in oceanography
at the University of Capetown (see "Massive Emissions..." in the bibliography).

For hundreds of years, the Namibian Coast has been
known for its hydrogen sulfide perfume. The fish kills, combined with
the satellite data, have made the giant belches a pressing subject of
scientific study.

The Namibian Coast has the most intense upwelling of
fertile deep-ocean water in the world, says Weeks, who collaborated on
the research with colleague Andrew Bakun and Bronwen Currie, a biogeochemist
with Namibia's National Marine Research and Information Center.

Mixed blessing Weeks explains that the shallow sea bottom along the
coast is covered with a thick ooze of decomposing diatoms -- free-floating
plants nourished by the strong upwelling. Upwelling generally makes great
fishing, and fishing is Namibia's third-largest industry, and second-largest
source of foreign exchange.

But there may be too much of a good thing. "As a
result of almost continual phytoplankton production," Weeks says, "there
is massive diatom fallout." Dead diatoms fall through the water, where
they are decayed by aerobic bacteria.

Anaerobic bacteria take over the decomposition task
in the thick, muddy sediment, producing hydrogen sulfide. When the gas enters the water column during an eruption, it separates into hydrogen and sulfur, and the hydrogen atoms combine with oxygen
to form water. That reaction removes oxygen from the water, creating deadly
low-oxygen conditions.

Double whammy Although
hydrogen sulfide is itself a respiratory toxin to fish and marine invertebrates, the reduced oxygen
may have greater ecological consequences in the long run, Weeks says.

Hydrogen sulfide that enters the atmosphere makes
"this awful, noxious smell of corroding metal," says Weeks. "But other
than the noxious smell and headaches, there are no known effects on the
human population."

Weeks and her colleagues tracked the eruptions with
the OrbView-2 SeaWiFS satellite. "The
surface is milky green due to the elemental sulfur," she says. When the
hydrogen sulfide oxidizes, it leaves sulfur at the surface water that
reflects visible light.

The low-oxygen conditions are not simply a transient,
local affair. Weeks followed one "event" out to sea, where it covered
20,000 square kilometers and lasted at least three weeks.

These hydrogen sulfide eruptions are the largest
in the world, Weeks adds. "Certainly you get hydrogen sulfide outgassing
in places like the Baltic Sea and the Black Sea, but the important thing
is that nowhere else does this actually happen remotely to the intensity
of Namibian waters, and yet it's completely natural."

Natural, perhaps, but given the stakes to the critical
fishing industry, and the suspicion that the eruptions may be getting
more frequent and intense, an international collaboration is starting
to examine possible links to global warming or other large ecological
disturbances.